In a cooling system of a vehicle, a safety cap of a radiator prevents a pressure from increasing above a reference pressure when fluid (cooling water, vapor, or air) in the cooling system expands according to a temperature increase to protect the cooling system when an engine starts. In addition, the safety cap prevents the pressure in the cooling system from decreasing below atmospheric pressure when the volume of fluid decreases according to cooling of the cooling system when the engine stops or supplements cooling water using such negative pressure.
In the above safety cap, as the means for realizing the above operation, a spring is mainly used to adjust a positive pressure (when discharged) and a negative pressure (when entered). A positive pressure valve is provided for preventing the volume of internal fluid from being increased when the cooling system is heated, and a negative pressure valve is provided for reducing the pressure (negative pressure) generated by volume reduction of internal fluid when the cooling system is cooled.
Here, in order to allow the positive pressure valve to perform its function when the positive pressure is applied, the cooling water must be secured when the volume of cooling water expands. Therefore, opening/closing of the negative pressure valve is adjusted by a spring for the negative pressure valve to prevent the negative pressure valve from being opened.
In the conventional safety cap, however, due to a spring force of the spring for the negative pressure valve, the negative pressure valve does not open smoothly, and thus, the negative pressure valve does not perform its function. In addition, when the negative pressure valve is not smoothly opened, the valve presses a seal (rubber) for long time so that the tackiness may be generated between the seal and the valve. Therefore, the cooling water is not supplied smoothly in the cooling system, thus distorting a hose. In particular, a venting function for air and vapor in the cooling system does not perform smoothly, thus deteriorating performance and reliability of the safety cap as well as reliability of the vehicle.
The above structure described as the background art is provided for only understanding the background of the present disclosure, however it should not be accepted that the present disclosure corresponds to the conventional art which has been already well-known to one having an ordinary skill in the art.